1. Field of the Invention
This invention relates to an image input apparatus for inputting image information, and more particularly, to an image input apparatus in which a single high-resolution still image is obtained by inputting and synthesizing a plurality of images.
2. Description of the Related Art
Recently, in accordance with the advent of high-performance or multimedia-type personal computers, multi-color or high-resolution monitors, and the like, there is an increasing demand for inputting high-resolution still images, such as documents, color drawings, photographs, and the like.
Although scanners have been widely used as means for inputting high-resolution still images, a number of disadvantages of scanners have been pointed out. For example, a great deal of time is required for scanners to receive data, and only plane images can be input. Accordingly, high-resolution cameras have recently been proposed in which various means are used instead of scanners.
Particular attention has been paid to cameras in which a high-resolution still image is input using a standard-resolution image input device. Such a standard-resolution image input device comprises a solid-state image pickup device, such as a CCD (charge-coupled device) or the like, having about four-hundred-thousand effective pixels. However, the resolution of such a device is insufficient for dealing with high-definition still images.
In order to deal with high-resolution still images using an image input apparatus including a standard-resolution image pickup device, a method (a pixel shifting method) has been proposed in which, for example, as shown in FIGS. 4(a) and 5, a plurality (four in this example) of image signals #0-#3 are obtained by shifting the optical axis of an image pickup element, comprising, for example, 4xc3x974 pixels, in units of a fraction of a pixel (in units of a xc2xd-pixel pitch in this example) in the horizontal and vertical directions, and these image signals are synthesized.
Another method (a picture-frame dividing method) has also been proposed in which, as shown in FIGS. 4(b) and 5, a plurality of image signals #0-#3 are obtained by dividing an image into a plurality of areas both in the vertical and the horizontal directions, and the image signals are synthesized to provide one picture frame by connecting borders of the sub-divided areas. In the pixel shifting method, a flat plane having parallel surfaces or a variable prism is generally used.
Next, an image input apparatus which can input a high-resolution image according to the above-described pixel shifting method will be briefly described with reference to FIG. 6.
FIG. 6 is a block diagram illustrating the configuration of an image input apparatus which can perform pixel shifting control. In this case, optical-axis shifting control in units of a xc2xd-pixel pitch is performed. In FIG. 6, a lens unit 701 has a function of changing the optical axis of the apparatus. Reference numeral 702 represents an image pickup unit. An image processing unit 703 performs various kinds of filtering processing. A memory unit 704 temporarily stores input image information. A memory input control unit 705 controls an input operation to the memory unit 704. A memory output control unit 706 controls an output operation from the memory unit 704. A lens control unit 707 controls the movement of the optical axis of the lens unit 701. An overall control unit 708 monitors the states of the respective other units, and controls operations and timings of the entire apparatus.
Next, the operation of the image input apparatus will be described. Before inputting an image, the lens unit 701 is controlled so that its optical axis is moved by the lens control unit 707. The memory input control unit 705 controls storage regions of the memory unit 704. First, input control of a still image is performed for an origin (a home position) in which pixel shifting is not performed in either the horizontal or vertical direction. An image signal input via the lens unit 701, the image pickup unit 702 and the image processing unit 703 is stored in a predetermined region of the memory unit 704 under the control of the memory input control unit 705. Thereafter, three additional image signals are input in the following sequence: a position is obtained by shifting the optical axis by a xc2xd-pixel pitch only in the horizontal direction, another position is obtained by shifting the optical axis by a xc2xd-pixel pitch both in the horizontal and vertical directions, and still another position obtained by shifting the optical axis by a xc2xd-pixel pitch only in the vertical direction (see FIG. 7). In the processing of inputting and storing the images, the memory input control unit 705 controls storage positions corresponding to respective image pickup positions. Four-frame pixel-shifting images, as shown in FIG. 5, obtained in the above-described processing are synthesized, and the obtained image is stored in the memory unit 704.
As result of the above-described processing, an image having a larger number of pixels than the number of pixels of a single solid-state image pickup device, i.e., a still image having higher resolution, is produced. In an image input apparatus which performs the above-described pixel shifting control, a great deal of time is required to input and store a plurality of image signals obtained by shifting pixels in fine units. For example, in order to input a high-resolution image obtained by shifting pixels in units of a xc2xd-pixel pitch in the above-described manner, several hundred milliseconds to several seconds is usually required.
However, in the above-described image input apparatus, a high-resolution still image cannot be correctly obtained if all image information cannot be normally input during a time period from the start of input of the first image signal to the completion of input of the last image signal due to various factors, such as the movement of the object to be input, vibration in the original mount or the main body of the apparatus, the interposition of a view-blocking obstacle, a noticeable change in illumination, or the like.
Since the above-described image input apparatus does not have means for detecting such an error in image pickup processing, it is impossible to detect if a normal high-resolution still image has been input. Accordingly, the user can confirm validity of image pickup operation only by visually confirming an actual image, for example, by displaying the obtained high-resolution still image on a monitor or printing the image. As a result, meaningless processing time is utilized, and reliability in image input operation is compromised.
The present invention has been made in consideration of the above-described problems.
It is an object of the present invention to provide an image input apparatus which can detect an incorrectly performed operation of receiving a high-resolution still image caused by predetermined factors, and which can determine invalidity of the obtained image information.
According to one aspect, the present invention which achieves the above-described object relates to an image input apparatus comprising image input means for converting an image of an object into an electrical image signal, storage means for storing a plurality of image signals input from the image input means, high-resolution signal forming means for forming a high-resolution signal by synthesizing the plurality of image signals stored in the storage means, comparison means for comparing the plurality of image signals with one another, and control means for controlling the formation of the high-resolution signal in the high-resolution signal forming means in accordance with an output of the comparison means.
Since the high-resolution signal is obtained by synthesizing the plurality of image signals, high-resolution image information can be obtained. Since the plurality of image signals are compared with one another and the formation of the high-resolution signal is controlled in accordance with the result of the comparison, it is possible to confirm easily if the plurality of image signals have been correctly input.
In one embodiment, the plurality of image signals stored in the storage means are cancelled in response to an output of the control means.
Since the plurality of stored image signals are cancelled in response to the output of the control means, unnecessary information need not be stored.
In another embodiment, a plurality of image signals are again input from the image input means and are stored in the storage means in response to an output of the control means.
Since the plurality of image signals can be reinput in response to the output of the control means, processing can be performed promptly when a plurality of image signals are invalid.
In still another embodiment, the image input means inputs a plurality of image signals obtained by shifting the optical axis of light from the object by a predetermined small unit (say, 1/n pixel, where n is a natural number) in at least one arbitrary direction and, if desired, in a direction perpendicular thereto.
Accordingly, images can be input according to a so-called pixel shifting method or a so-called picture-frame dividing method.
In yet another embodiment, the image input means comprises an image pickup device for performing photoelectric conversion of the light from the object imaged onto a photosensing surface thereof via a lens, a flat plate made of a light-transmitting material provided on the optical axis so that its angle of inclination is variable, and position control means for controlling an imaging position of the light from the object by changing the angle of inclination of the flat plate.
Accordingly, when using the pixel shifting method, a plurality of image signals can be easily extracted.
In yet a further embodiment, the image input means inputs a plurality of image signals obtained by dividing the picture frame of an image in an arbitrary direction and, if desired, in a direction perpendicular thereto.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings.